Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method of determining cell coverage for a device-to-device (D2D) operation performed by a terminal in a wireless communication system and the terminal using the method.
Related Art
In International Telecommunication Union Radio communication sector (ITU-R), a standardization task for International Mobile Telecommunication (IMT)-Advanced, that is, the next-generation mobile communication system since the third generation, is in progress. IMT-Advanced sets its goal to support Internet Protocol (IP)-based multimedia services at a data transfer rate of 1 Gbps in the stop and slow-speed moving state and of 100 Mbps in the fast-speed moving state.
For example, 3rd Generation Partnership Project (3GPP) is a system standard to satisfy the requirements of IMT-Advanced and is preparing for LTE-Advanced improved from Long Term Evolution (LTE) based on Orthogonal Frequency Division Multiple Access (OFDMA)/Single Carrier-Frequency Division Multiple Access (SC-FDMA) transmission schemes. LTE-Advanced is one of strong candidates for IMT-Advanced.
There is a growing interest in a Device-to-Device (D22) technology in which devices perform direct communication. In particular, D2D has been in the spotlight as a communication technology for a public safety network. A commercial communication network is rapidly changing to LTE, but the current public safety network is basically based on the 2G technology in terms of a collision problem with existing communication standards and a cost. Such a technology gap and a need for improved services are leading to efforts to improve the public safety network.
The public safety network has higher service requirements (reliability and security) than the commercial communication network. In particular, if coverage of cellular communication is not affected or available, the public safety network also requires direct communication between devices, that is, D2D operation.
D2D operation may have various advantages in that it is communication between devices in proximity. For example, D2D user equipment (D2D UE) has a high transfer rate and a low delay and may perform data communication. Furthermore, in D2D operation, traffic concentrated on a base station can be distributed. If D2D UE plays the role of a relay, it may also play the role of extending coverage of a base station.
A UE (a terminal) may perform a D2D operation using resources controlled by a network (for example, a base station) if the UE locates in a network coverage and perform a D2D operation using preconfigured resources if the UE locates out-of-the network coverage. That is, the resources to be used for the D2D operation may be different according to whether or not the UE is located in the network coverage. In this sense, the determination of the network coverage is important.
The case where network coverage is temporarily lost may occur while a terminal is within network coverage. For example, if the terminal fails to obtain system information that a network temporarily provides or fails to temporarily synchronize with the network, the terminal may determine the network coverage as being temporarily lost. In this case, the terminal hastily declares that the terminal deviates from the network coverage and changes a resource for the D2D operation. This may cause continuity and reliability problems of the D2D operation. For example, this is the reason why the terminal needs to change a resource for the D2D operation again if the terminal recovers a temporary network coverage loss.
In the case where the terminal performs the D2D operation, there is a need for a reliable method of determining the network coverage and a terminal using the method.